Watch four routers find each other, share a map of the network, and compute the best paths.
OSPF (Open Shortest Path First) is a routing protocol used inside one organization’s network, such as a campus, a data center or an ISP’s core. Routers discover their neighbors, share what they know about their own links, and each one builds the same map of the network. Then every router calculates the cheapest path to every destination for itself. That makes it a link-state protocol and an interior gateway protocol (IGP).
Why it matters. It replaces hand-typed static routes and reroutes around failures automatically, in seconds. It is one of the most common routing protocols in enterprise and service-provider networks.
How to use this lab. Press Next to step through. Tap a router to see its tables, and use the tabs below the map (they switch automatically as the story moves). Try the Break it scenarios.
Where it fits. Learn OSPF before BGP. OSPF finds paths inside a network, while BGP connects separate networks to each other.
Simplified on purpose: every link is point-to-point inside area 0 (so no DR/BDR election), the costs are made up (real costs usually come from interface bandwidth), and the timers are the common defaults of a 10 second Hello and a 40 second dead interval. The routers follow the real OSPF steps: Hello, 2-Way, ExStart/Exchange, Loading, Full, then SPF.